1. Field of the Invention
The invention is directed to a pulse dampener for high pressure liquid chromatography comprising a unitized plug having two portions, each portion having different compressibility characteristics.
2. Description of the Prior Art
In high pressure liquid chromatography a chromatographic column is connected by a suitable conduit to a reciprocating type pump that operates to transmit a liquid vehicle from a supply reservoir. The liquid vehicle is transmitted through a pulse dampener and then transmitted to an injection valve wherein a liquid sample is entrained in the liquid vehicle. The liquid vehicle and sample are then transported through the chromatographic column for determination of the constituents of the sample. The liquid vehicle is usually a chemical solvent which is non-reactive with the sample, and neither the sample or the solvent are reactive with the material from which the column is packed.
In chromatographic systems the solvent flow paths should have minimal internal volume and be well swept to afford continuous movement of the liquid solvent and sample through the system. This is important in solvent changeover and gradient chromatography techniques. If excessive internal volume exists it tends to cause mixing which is detrimental to efficient solvent changeover and causes loss of predictable time-based solvent proportions in gradient work.
Various types of pulse dampeners have been developed for various purposes. U.S. Pat. No. 3,333,604, discloses a pulse dampener for use in a high pressure car washing equipment. Other examples of fluidic pulse dampeners are disclosed in U.S. Pat. Nos. 2,216,374, 2,354,201, 2,808,070, 3,851,661 and 4,452,069.
U.S. Pat. No. 2,883,180, discloses a hydraulic accumulator formed of a rubber spring. In selected embodiments the rubber springs are provided with a thick diaphram that maybe formed of synthetic rubber or a rubber like material.
Pulse dampeners have also been developed for chromatography systems, as disclosed in U.S. Pat. Nos. 4,163,461 and 4,186,776. Each of these dampeners is provided with a bulbous shaped cavity having a flexible diaphram arranged across the cavity. One side of the diaphram is exposed to the fluid pumped by the reciprocating pump while the other side is exposed to a compressible fluid.
In U.S. Pat. No. 3,984,315, a pulse dampener has been prosed wherein a flexible diaphram extends across a cavity. One side of the diaphram is exposed to the fluid from the reciprocating pump and the other side is provided with a coil spring that is positioned to resist flexing of the diaphram.
In high pressure liquid chromatography dampeners maybe formed of a plastic spool having an axial bore to receive liquid from the pump. The spool is preferably made of polytetrafluoro-ethylene which is chemically inert to the fluids typically used in liquid chromatography. The spool is encased in a stainless steel cylindrical housing which is filled with a compressible liquid. Such a dampener is disclosed in U.S. Pat. No. 4,222,414. In U.S. Pat. No. 4,024,061, a pulse dampener has been proposed that comprises a block of solid material, such a polytetrafluoro-ethylene, which occupies 99% of the volume of a cavity. See also U.S. Pat. No. 4,045,343.